Across Syria, Violent Day of Attacks and Ambush

BEIRUT, Lebanon — Violence raged across Syria on Sunday as government forces killed dozens of rebels in an ambush east of Damascus, fighters linked to Al Qaeda battled Kurdish militias and Syria’s military peppered an outdoor market with mortar rounds.

Antigovernment activists also accused government forces of killing 13 members of a family in northwestern Syria.

In the day’s deadliest attack, government forces ambushed a group of rebel fighters in the town of Adra, northeast of Damascus, and left dozens of dead bodies lying in the sand, according to video broadcast on Al Manar, a television station run by Hezbollah, the Lebanese militant group and political party that supports President Bashar al-Assad.

The Syrian Observatory for Human Rights, an anti-Assad group based in Britain that tracks the conflict through a network of contacts on the ground, said 49 rebels were killed in the attack.

It was another blow to the rebel movement. The momentum in the civil war has shifted in favor of Mr. Assad, whose forces have rolled back a number of rebel gains near Damascus, the capital, and elsewhere. Infighting among rebels who took up arms to topple Mr. Assad has allowed his forces to solidify their hold on central Syria and gradually expand their reach.

Skirmishes between groups are increasingly common, and many fighters have gotten bogged down in local turf wars.

Clashes have been raging for days across the ethnically mixed strip of land along the northern border with Turkey, pitting mainstream rebels and extremist groups linked to Al Qaeda against Kurdish militias. The Kurds, Syria’s largest ethnic minority, seek greater control of their own areas and fight to keep the rebels out.

On Sunday, Kurdish fighters surrounded the local leader of one of the groups linked to Al Qaeda, the Islamic State of Iraq and Syria, inside a school he and his fighters were using as a base near the border town of Tel Abyad. Activists said the Kurdish fighters did not storm the school to detain the group’s leader, who is known by the nom de guerre Abu Musab, because they feared he would blow up the school.

To push the Kurds to grant him safe passage, rebels and the group’s fighters detained hundreds of Kurdish civilians. The two sides finally reached a deal and the group’s leader was released in return for the 300 detained Kurdish civilians, according to the Syrian Observatory group.

Syria’s Kurds have used the erosion of state control during the civil war to push for greater autonomy in their areas. This has increased tensions with the area’s rebel fighters, many of whom hope to found an Islamic state. Other rebel groups resent the extremists who have joined the fight in Syria to serve their own ends.

Similar clashes between Kurds, rebels and extremists continued near Ras al-Ain in Hasaka Province, activists said.

In the northern city of Ariha, government forces fired mortar rounds into a market on Sunday, killing at least 23 people, some of them women and children, the Syrian Observatory reported.

Along the Mediterranean coast, opposition activists said, 13 members of a family in Bayda, another area where the war has heightened sectarian tensions, were killed. The account could not immediately be independently confirmed.

The Syrian Observatory said four women and six children were killed inside a home, and three men were slain nearby. A man unrelated to the family was found dead in a nearby field.

The coastal Syrian province of Tartus is heavily populated with minorities, mostly Christians and Alawites, the offshoot of Shiite Islam to which Mr. Assad belongs.

The area has suffered less violence than other parts of Syria, and many Syrians from elsewhere have sought refuge there.

But the fighting there has caused tensions with the area’s Sunni Muslims, who are a minority in the region but a majority in Syria and form the core of the anti-Assad movement. Many residents fear that their Sunni neighbors support the rebels.

The Syrian Observatory said that clashes between rebel and government fighters had raged nearby overnight, killing fighters on both sides, and that the government held a mass funeral in Tartus on Sunday for 30 fighters killed in battles with rebels.

A version of this article appears in print on , on Page A7 of the New York edition with the headline: Across Syria, Violent Day Of Attacks And Ambush. Order Reprints | Today’s Paper | Subscribe